The present invention relates to a keyed cylinder assembly for a door lock and, more particularly, to a keyed cylinder assembly including a keyed cylinder that allow insertion of either a first key capable of unlatching both a latch bolt and a deadbolt of the door lock or a second key capable of unlatching the latch bolt only.
Typical mortise locks include a latch bolt and a deadbolt both mounted in a case to lock a door to which the lock is mounted. Generally, the mortise locks further include a keyed cylinder to allow operation of both the latch bolt and the deadbolt from the outdoors by using a key. In mortise locks for use in hotel room doors, the keyed cylinder is required to cooperate with two different keys known as a master key and a service key, allowing a holder, such as a hotel manager, of the master key to operate both the latch bolt and the deadbolt from the outdoors while a holder, such as a room guest, of the service key can operate only the latch bolt from the outdoors. In a case that the room guest is intended to stay longer but refuses to pay the current bill, the hotel manager may move the deadbolt to a locking position with the master key to prevent the room guest from entering the room before the current bill is paid up. Thus, not only the payment problem of the room guest can be solved but also the possibility of burglary resulting from copied or lost service keys can be reduced. In such an operation mode allowing the deadbolt to be unlocked by the master key but not by the service key, a keyed cylinder with a special mechanism is required in which the service key can only rotate a cylinder plug of the keyed cylinder in a restricted angular range while the master key can rotate the cylinder plug 360 degrees. However, structures of the keyed cylinders of mortise locks are generally complicated, resulting in assembling difficulties, frequent malfunction, and increased costs.
Thus, a need exists for a keyed cylinder that can be operated by either a master key capable of unlatching both a latch bolt and a deadbolt of a door lock or a service key capable of unlatching the latch bolt only while having simplified structure and allowing smooth operation by the master and service keys.